Papua New Guinea's Mount Ulawun volcano - designated one of the world's most hazardous - began spewing ash on Wednesday, turning the sky black and prompting authorities to warn of a possible eruption.
The volcano, located on the remote Bismarck Archipelago, is listed as one of 16 "Decade Volcanoes" targeted for research because they pose a significant risk of large, violent eruptions.
"The volcanic activity at Mt Ulawun began at 07:00 this morning after slight rumbling and light emission," Leo Porikura, an official with the West New Britain Disaster Office, told AFP.
"The Rabaul Volcano Observatory has declared a stage one alert warning of a possible eruption of Mt Ulawun Volcano."
Witnesses reported ash spewing high into the air, sending trails that spanned across the sky for kilometres.
"The sky has turned black," said Kingsly Quou, the manager of the nearby Mavo Estates, a palm plantation, adding that villagers had already been evacuated from the foot of the volcano.
Thousands of people live in the shadow of Ulawun, despite it being one of the most active volcanoes in the country.